This 1973 volume reports the proceedings of a symposium held at the University of Reading in 1971. The main purpose of the symposium was to consider the relative biological efficiency of alternative methods of protein production by both plants and animals, at the level of tissue, the individual and the population, in a variety of environments. Although the main contributions deal with an agricultural framework, emphasis is placed on understanding the underlying biological processes. Introductory sections highlight the wide scope of the subject, the reasons for concern about protein production and the meanings that should be attached to the term biological efficiency. To provide further background to the discussions, economic and social aspects of protein production are considered. Since the primary intention was to achieve a synthesis of all the contributions, the book also contains the reports of discussion leaders who were invited to the guide.